The present invention relates to a medical instrument which may be structured in either of two similar forms to provide an electrode or a surgical cutting tool. In a preferred form of the invention, the same comprises an improved bipolar electrode structure adapted to be inserted through the vagina and cervix of a woman in labor and into contact with the fetus. The distal end of the device includes an electrode structure having two electrodes, a first of which is arranged to engage the tissue or skin of the fetus by remote manipulation of such first electrode. The two electrodes may be connected through suitable wires to an amplifier and a cardiotachometer for recording the fetal electrocardiogram and heart rate during labor and delivery.
In a second structural form, a surgical tool is substituted for the first electrode and can be similarly remotely manipulated for removing a piece of tissue from within a cavity of the body for purposes of performing a biopsy thereon.
While not intending to be limited thereby, the invention and background thereof will be described with respect to the preferred bipolar electrode structure form.
Various forms of electrodes for monitoring purposes have been devised. The structures typically include one or more electrodes, electrical conductors connected therewith, and means for facilitating insertion of the electrode or electrodes within the body. Notable examples of such devices are found in Hunter et al U.S. Pat. No. 3,120,227, La Croix U.S. Pat. No. 3,580,242, Ruttgers U.S. Pat. No. 3,750,650 and Hon et al U.S. Pat. No. 3,827,428. One of the problems associated with attempts to monitor fetal heartbeat and the like is that of properly attaching the electrode to the fetus. In a bipolar electrode structure, two electrodes are used, one of which is attached to the fetus, and the other of which usually is disposed in the vaginal fluid and serves as a reference electrode. The two electrodes typically are of predetermined surface area and sometimes have a predetermined spacing between the two. While the second electrode generally presents no problem from the standpoint of the placement thereof, the first electrode does. The aforementioned Hunter patent shows an electrode in the form of a "C", the ends of which may be closed to engage the tissue by moving a plastic sleeve over the electrode. The La Croix patent discloses an arrangement wherein the first electrode has a fish-hook configuration. The Ruttgers patent discloses an electrode structure wherein the first electrode is in the form of a double helix which is screwed into the tissue. The Hon et al patent discloses an electrode structure wherein the first electrode may be in the form of a point and an auxiliary sharpened helix facilitates attachment thereof to the tissue, and discloses an electrode structure wherein the first electrode is in the form of a single helix which can be screwed into the tissue. The Hon et al patent discloses an electrode structure which is an improvement over certain prior electrodes in that ready insertion of the electrode structure and attachment of the first electrode to the fetus is possible.
The bipolar electrode structure in operation provides a path for current, from the monitored fetus to the recording equipment, with a magnitude very small, such as only milliamps. Noise interference problems have been substantially overcome by making a bipolar electrode structure through injection molding techniques. An example of such techniques and an electrode manufactured thereby is described in applicant's copending application Ser. No. 366,701, filed June 4, 1973, entitled "A Method of Making A Bipolar Electrode Structure", now U.S. Pat. No. 3,890,420. A prior are difficulty of making suitable bipolar electrode structure was the criticality of the exposed surface area ratio between the first electrode and the second electrode. It has been determined that the exposed surface area of the second electrode preferably is twice that of the exposed surface area of the first electrode. If this surface area ratio is substantially varied, the signal-to-noise ratio of the system becomes a significant inhibiting factor in the monitoring operation. This difficulty has been substantially overcome in accordance with the molding techniques and structure described in said copending application.
Although improvements have been made in preventing the helical type first electrode from piercing the fetal epidermis too far because of the electrode structure and manual driving arrangement therefore, it has been found that it still is possible in some instances to screw the helix type electrode too far into the fetus, possibly resulting in tearing or removal of fetal tissue.
On the other hand, in the preferred form of the present invention, the electrode structure includes a first electrode which is pointed and which may be remotely controlled to pivot with respect to a stationary block. With this arrangement, the distal end of the structure containing the stationary member and pointed first electrode is essentially "closed" during insertion into the body, and then may be "opened" by remote activation, to be described below, to cause the first electrode to engage the fetal epidermis but without allowing excessive penetration.
In a preferred form of the present invention, the same includes an elongated and curved guide tube. A plug structure is disposed at the distal end and comprises the electrode assembly having the stationary member and the pointed and pivotal first electrode. The electrode assembly also includes the second or reference electrode, and this entire assembly is encapsulated in plastic to form a unitary plug structure. This electrode structure is disposed in the distal end of the guide tube, and wires from the two electrodes extend through the guide tube to the proximal end of the guide tube. The doctor inserts the distal or forward end of the curved guide tube, including the electrode assembly, through the vagina of the mother and cervix until the first electrode and the block assembly make contact with the fetal head or other portion of the fetus.
A ratchet and cam assembly is disposed on the proximal end of the guide tube and engages the wire connected to the first electrode. By moving a lever, this wire essentially is "pulled" to cause the first electrode to pivot away from the stationary member of the electrode assembly. Once the fetus is contacted, the lever can be moved to allow the first electrode to pivot or spring back to its normal position to thereby physically engage and couple with the fetus. In this manner the end of the first electrode, which may be pointed, pierces the tissue of the fetal epidermis and makes good electrical and mechanical contact therewith. Once the electrode structure is attached to the fetus, the guide tube and the ratchet and cam assembly on the proximal end thereof are removed from the mother, thereby leaving only the bipolar electrode assembly and the wires connected therewith. The entire apparatus is disposable after use.
In the alternative form of the invention as mentioned earlier, the second electrode is not necessary, and the first electrode is replaced by a surgical cutting tool. A wire, cable or other suitable flexible connecting means is connected between the support for the surgical tool and the ratchet and cam arrangement. This enables the surgical tool to be moved away from the stationary member by movement of the lever of the ratchet and cam arrangement, and to return toward the stationary member for engaging, cutting and removing a piece of tissue for biopsy purposes.